Manufacturing method for a plastic element

Abstract

The present invention relates to a method and a mould for manufacturing plastic element as well as a plastic element having oppositely arranged eye parts where oppositely one eye part in relation to a substantially centrally placed stem is arranged a recess on the opposite side, where the manufactured plastic elements for example are chain links or a conveyor belt, and where the mould comprises two mould halves, where each part comprises protruding core parts and further a plastic element manufactured by the mentioned method of manufacture in the mentioned mould, where in the eye parts are provided through-going openings in the chain links with respect to the travel direction.

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method as well as a mould system for the manufacturing of plastic elements as well as a plastic element, said element having oppositely offset eye parts, where oppositely one eye part on one side of a stem is arranged a recess on the opposite side, where the manufactured plastic elements for example are chain links for conveyor belts and where the mould system comprises two mould halves such that each mould half comprises extending core parts, where the core parts are made with a taper and further that each plastic element manufactured by the method and by the mentioned mould system is a chain link, which is suitable for being assembled with other corresponding or identical chain links in order to create a flexible conveyor belt, where the element comprises a stem on both sides of which eye parts are arranged such that directly opposite an eye part on one side of the stem is arranged a corresponding recess on the opposite side such that two identical elements can be brought together and in this manner comprise overlapping eye parts such that a through-going aperture is provided in the chain link's transverse width direction.

BACKGROUND OF THE INVENTION

[0002] Chain links are among other things used for constructing conveyors, which conveyors are relatively stiff in one dimension, usually the width, whereas they are very flexible in the transport direction. Furthermore, it can be achieved that the conveyor is very flexible for deflections in the conveyor's transport plane.

[0003] Conveyors as well as chain links as described above are known from for example U.S. Pat. No. 6,216,854. The known conveyors are constructed by assembling a number of chain links which are mutually connected, where each chain link consists of a stem oriented in a transverse direction to the transport direction of the conveyor, and protruding from the stem in the plane of the conveyor eye parts are arranged. In every eye part perpendicular to the transport direction, approximately in the middle of the chain links' thickness, is arranged a through-going aperture. Furthermore, the protruding eye parts on both sides of the stem are arranged in a offset manner, such that on one side of the stem an eye part is formed and directly opposite the eye part on the other side of the stem a recess is provided. By means of this construction two chain links can be assembled such that the eye parts on one side of the stem fit into the recesses of an adjacent chain link. When assembling the chain links in this manner, the apertures formed in the eye parts in the thickness dimension will overlap such that one aperture is formed through the two assembled chain links transverse to the conveyor's transport direction. In order to assemble the chain links into a conveyor belt, an assembly pin is inserted into the overlapping apertures. If the aperture has an oval shape, it is possible for each separate chain link to move relatively to the adjacent chain links and at the same time stay connected to said chain links by means of the inserted assembly pins. Typically, the pin is a steel axle.

[0004] Due to this possibility of relative displacement between two adjacent chains links, it becomes possible for the conveyor to be side-flexible in a direction parallel to the plane of the conveyor. Furthermore, as each chain link can rotate around the inserted assembly pin, the conveyor obtains a large degree of flexibility in a plane perpendicular to the conveyor's traveling direction.

[0005] The manufacture of this type of plastic element is usually carried out by a plastic molding process, for example injecting molding, where the element is cast in a lying position. By lying is in this connection to be understood that the mould is shaped such that when the two halves of the mould are closed and forced together, each separate chain link is cast such that the transport plane of the chain link, i.e. the plane where an assembly of elements constitute a conveyor belt, is perpendicular to the closing direction of the mould. After closure of the two mould halves, but prior to injection, a number of pin bolts are inserted into the mould corresponding to the number of apertures which need to be formed in each chain link in order to provide the apertures in the thickness dimension for the later assembly of the chain links into a conveyor as discussed above.

[0006] After insertion of the pin bolts into the plastic mass, the mass is introduced into the mould under high pressure, just as the two mould halves are forced together with a very high pressure, typically from about fifty to hundreds of tones. With this pressure a number of chain elements can be formed in each mould. This means that more elements are manufactured in one molding cycle. After the plastic mass has been forced into the mould, the pin bolts are withdrawn. Next the two mould halves are moved apart and the finished plastic elements are thereby released.

[0007] The dimension of moulds for this type of element is relatively large as the mould consists of the width of the elements plus the length of the pin bolts, which usually corresponds to the width of the elements, since one pin bolt has to create openings throughout the eye parts in the entire width of an element in the thickness dimension in order to be able to assemble the chain links into a conveyor belt as discussed above. Furthermore, in the end of the pin bolts it is necessary to arrange hydraulic cylinders which can insert the pin bolts and withdraw the pin bolts again after the plastic mass has been introduced into the mould. Hereby the space requirements for the mould is substantially larger than the size of the element. Furthermore, it is necessary to provided a large force in order to force the two mould parts together, since the surface area of the elements in the mould's closing surfaces multiplied by the pressure in the plastic mass during the casting process result in a large pressure, which influences the mould halves with a relatively large resulting surface due to the orientation of the elements in the mould.

[0008] A similar casting process as discussed above with reference to the background art document U.S. Pat. No. 6,216,854 is disclosed in WO 9738925. This conveyor is especially produced for providing good cooling to products placed on the conveyor. Therefore, the surface of the conveyor is perforated with rather large perforations such that the air easily can flow through the surface of the conveyor. During the molding process, which is carried out according to the principles described above with respect to U.S. Pat. No. 6,216,854, the two mould halves are brought into contact in order to provide the large recesses in the surface of the chain links. The apertures for inserting assembly pins as described above are manufactured in exactly the same way as the chain links disclosed in U.S. Pat. No. 6,216,854 and further the element is arranged in the mould, i.e. lying, as disclosed above.

SUMMARY OF THE INVENTION

[0009] One object of the present invention is to improve and simplify the moulds for the casting process and the same time reduce the requirements to the size of the injection mould machine.

[0010] This is achieved according to the present invention with a method which is particular in that

[0011] the mould for the molding process comprises two halves with protrusions/core parts which are moved into a position where the protrusions/core parts are arranged in a side-by-side manner prior to injecting the molding material;

[0012] that the protrusions/core parts on one mould half create the recesses between neighboring eye parts on one side and the cavity inside the oppositely arranged eye parts on the other side of the stem;

[0013] that the ultimate ends of the protrusions/core parts on a first mould half during closing/injection are brought into contact with the side-by-side arranged interior ends of the protrusions/core parts on the other mould part, and

[0014] that the mould halves after injection of mould material are withdrawn, whereby a through-going aperture through the eye parts in the chain links width direction is created.

[0015] In the description of the moulds above, ultimate end and interior end of the protrusions/core parts shall be understood such that the cores protrude from the mould base. The mould base is adjacent the interior part within the terminology used in this application and the ultimate end of the core is therefore the pinnacle of the protruding protrusion/core part, i.e. the part of the protrusion/core part furthest from the base.

[0016] Further, where reference is made to the traveling direction of the conveyor. This is understood as the direction in which the conveyor will transport goods placed on said conveyor.

[0017] The chain links have a top side on which the goods to be transported on the conveyor will be placed. The bottom side is opposite the top side. In relation to the transport direction of the conveyor or the direction perpendicular to the traveling direction is the width of the conveyor or chain link respectively.

[0018] By designing the moulds such that the cores for the eye parts in a first mould half are offset in relation to the second mould half, where the cores have corresponding side surfaces which during the casting process are in abutment such that the mould in its closed condition has contact points between the two mould halves. The pin bolts which in the prior art created the apertures in the third dimension become superfluous. This results in a number of advantages. As the pin bolts neither need to be inserted nor drawn back, a molding cycle can be completed faster and consequently there is a substantial saving in time by being able to cast the elements directly without the intermediate process of inserting, respectively removing, the pin bolts and furthermore the injection molding machine can be manufactured cheaper in that the mould is substantially smaller and therefore does not require a large injection molding machine.

[0019] As discussed above traditional moulds have a size corresponding to the width of the elements plus the length of the pin bolts plus the hydraulic cylinders necessary in order to be able to insert and withdraw pin bolts in order to create the apertures in the third dimension. According to the method of the present invention the pin bolts as well as the hydraulic cylinders can be excluded such that the entire mould size substantially corresponds to the width of the elements. Hereby it becomes possible to utilize substantially smaller injection molding machines which in turn results in substantially lower production costs. Furthermore, the mould themselves become cheaper to manufacture in that they are smaller.

[0020] Yet another advantage achieved by being able to not use pin bolts in order to create the apertures in the third dimension is achieved in that pin bolts used in traditional moulds for forming of the apertures become worn. During the injection molding process and during the hardening under high pressure the plastic has a tendency to creep up to 2%. This creep will cause the plastic to adhere to the pin bolts and due to the withdrawal of the pin bolts this will cause wear on the pin bolts. This friction wear on the pin bolts means that the apertures in the elements will have a varying size during the production process whereby the tolerances between separate chain links will vary which can have substantial influence on the life expectancy of the finished conveyor belt. Furthermore, the wear on the pin bolts can result in that the apertures in each element can vary and possibly induce casting errors in the eye parts of the elements which can also influence the function of the conveyor belt in a negative direction.

[0021] In a preferred embodiment of the invention the plastic elements are arranged in the mould such that the elements are placed standing up during the injection molding process in relation to the closing direction of the mould. Within the scope of the present invention, standing up shall be understood as the plane wherein the elements in the use condition, i.e. if chain links as discussed above are being produced, will be assembled (the transport plane) in order to constitute an conveyor. Standing up will therefore be the transport plane of the finished conveyor. This plane is perpendicular to the thickness plane as well as the width plane of the elements. By the width of an element is understood the width of a conveyor belt assembled from chain links.

[0022] Furthermore, by producing the elements where these are standing up during the injecting molding process the closing pressure on the moulds can be substantially reduced in that the surface (the thickness/width of the element which creates the counter pressure on the mould halves) can be substantially reduced in comparison to the traditional method, where the length/width of the elements will determine the closing pressure of the mould.

[0023] A plastic element according to the invention is substantially different from the known type of chain link in that the stem is penetrated approximately in the middle of the thickness direction, so that from a recess on one side of the stem an opening through the stem into the oppositely positioned eye part is created. The stem with the breakthroughs still have the necessary strength, but a substantial savings on materials is achieved in that the stem in the thickness direction of a plastic element according to the invention is comparable to a lattice structure. This lattice structure comprises the plastic elements' outer surfaces and interior connection members which are arranged between the outer surfaces of the plastic element and is placed between recesses and oppositely arranged eye parts. The said connection members constitute the limits of the through-going apertures in the eye parts towards the stem part.

[0024] From WO 97/38925 is disclosed a chain link, a conveyor chain and a method for producing said chain links. In the method for manufacturing the chain links, the chain links are in the lying down position and the mould parts are brought together in order to create the large apertures perpendicular to the conveyor belt's traveling direction. These apertures are provided in order to be able to have a large flow of air through the conveyor belt in order to cool objects placed on the conveyor belt. For producing the apertures in the eye parts, traditional pin bolts are used with the inherent problems as discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] A more complete appreciation of the invention and many of the intended advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considering the connection with the accompanying drawings, wherein:

[0026] FIG. 1 is a perspective view of a conventional chain link;

[0027] FIG. 2 illustrates a perspective view of a chain link according to the invention.

DESCRIPTION OF EMBODIMENTS

[0028] Referring to the drawings, wherein like reference numerals designate identical or corresponding parts throughout and in particular in FIG. 1, there is shown a chain link produced according to the traditional method. The element 1 has a stem 2 from which eye parts 3 protrude in the traveling direction of the conveyor belt. Due to different requirements recesses 4 can be arranged in the eye parts 3 perpendicular to the surface which constitutes the conveyor belt. In order to be able to assemble more chain links into a conveyor belt, apertures 5,6 are arranged in the thickness dimension of the chain link perpendicular to the transport direction of the conveyor belt and approximately in the middle of each chain link's thickness dimension through respectively the protruding eye parts on one side on the stem and on the other side of the stem. In the illustrated example the aperture 5 on one side of the stem is in the shape of a circular hole, while the apertures 6 on the other side of the stem are in the shape of elongated holes.

[0029] When assembling two identical chain links 1 the eye parts with round holes are inserted in-between the eye parts with elongated apertures. In this manner an overlap between the round holes 5 and the oval aperture 6 is achieved. Through the overlapping apertures a round axle is inserted, said axle having an outer dimension substantially corresponding to the diameter of the holes 5. Due to the shape of the elongated holes 6 the chain links will be able to move relatively to each other in the conveyor belt's transport direction. Furthermore, the chain link may be sideways flexible in the plane of the conveyor belt.

[0030] In FIG. 2 is illustrated the corresponding element as illustrated with respect to the description of FIG. 1, but manufactured according to the method disclosed in the present invention. Like reference numbers is a factor 10 larger than in FIG. 1.

[0031] In the illustrated example recesses are created in the eye parts 30 perpendicular to the plane of the conveyor belt. From the stem 20 project eye parts 30 offset arranged such that on one side of the stem 20 is arranged an eye part 30 and directly on the opposite side of the stem a recess 70 is provided. As explained above with reference to FIG. 1 a number of elements 10 can be assembled to a conveyor belt by inserting the eye part 30 into the recess 70 and thereafter insert an axle through the overlapping openings 50,60. In this manner a flexible conveyor belt can be constructed exactly as explained above with reference to FIG. 1.

[0032] The mould according to the invention for manufacturing of the elements, for example as illustrated with reference to FIG. 2, will have engaging surfaces between the two mould halves corresponding to the openings 50,60. Where the mould closing direction for an element produced as described with reference to FIG. 1 is illustrated by the arrow 8, the corresponding closing direction with respect to the new inventive method according to the invention is illustrated with the arrow 80.

[0033] As is evident from FIG. 2 the surface which created the counter pressure when closing the two mould halves will be substantially less in that it will only be the width of the eye parts multiplied by the thickness of the element which will create the counter pressure against the mould halves, whereas with the manufacturing process for an element as illustrated in FIG. 1 it will be the entire surface of all the eye parts 3 as well as the stem 2 which will create the counter pressure against the mould halves.

[0034] Contrary to the process known from the above mentioned document WO 97/38925 it is possible with the manufacturing process according to the present invention to manufacture chain links which have a solid surface and still benefit from the manufacturing process as described above. The chain links known from WO 97/38925 will inherently, as a result of the process disclosed in the document, be provided with apertures in order to provide the cooling necessary for that process.

[0035] Above the invention has been described with respect to chain links, which chain links by assembling a number of corresponding or identical chain links can be made into the shape of a flexible conveyor belt. It should, however, be understood that the invention is not limited to chain links of the type mentioned above, but the method for manufacturing of plastic elements according to the invention can be utilized in other plastic element producing processes, where recesses in three dimensions are needed and which are to be manufactured in a great number.

[0036] The method according to the invention is especially developed with respect to plastic molding processes such as injection molding of plastic, but can also be used in other plastic forming processes where moulds comprising two parts are used.

[0037] Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appending claims the inventions may be practiced otherwise as specifcally described herein.

Claims

1. Method for manufacturing of plastic elements having oppositely arranged offset eye parts, wherein there oppositely to an eye part on one side of a stem is arranged a recess on the opposite side; where the manufactured plastic elements for example are chain links for a conveyor belt and where the method comprises;

that the mould for the molding process comprises two halves with protrusions/core parts which are moved into a position where the protrusions/core parts are arranged in a side-by-side manner prior to injecting the molding material;

that the protrusions/core parts on one mould half create the recesses between neighboring eye parts on one side and the cavity inside the oppositely arranged eye parts on the other side of the stem;

that the ultimate ends of the protrusions/core parts on a first mould half during closing/injection are brought into contact with the side-by-side arranged interior ends of the protrusions/core parts on the other mould part, and

that the mould halves after injection of mould material are withdrawn, whereby a through-going aperture through the eye parts in the chain links' width direction is created.

2. Method for manufacturing of plastic elements by plastic molding according to claim 1, wherein the mould halves are shaped such that the elements are molded having the closing direction of the mould halves parallel to the elements' longitudinal direction/conveyor belt's transport direction.

3. Mould for manufacturing elements in a plastic molding machine according to claim 1 and/or 2, wherein the mould comprises two mould halves, where each half comprises protruding mould parts, where the mould parts have a taper and wherein the core parts in a first mould half are offset in relation to the other mould part such that the core parts have corresponding ultimate side ends which during molding are in engagement.

4. Mould for manufacturing elements in a plastic molding machine according to claim 3, wherein the ultimate side edges on the protrusions/core parts on a first mould half in the mould's closed position correspond to offset interior side surfaces on the protrusions/core parts on the other mould half.

5. Element manufactured by a plastic molding process in a two-part mould according to any of claims 1-4, where the element is a chain link, which chain link can be assembled with other corresponding or identical chain links and thereby create a flexible conveyor belt, where the chain link comprises a stem on both sides of which perpendicular to the transport direction of the chain link eye parts are provided such that directly opposite an eye part on the other side of the stem is arranged a corresponding recess such that two identical chain links can be pushed together and thereby have overlapping eye parts and where in the eye parts are arranged through-going apertures in the chain links with direction, wherein the stem is broken through such that from a recess on one side of the stem is created an opening into the oppositely arranged eye part on the other side of the stem.