Pipe having a socket and an apparatus for making same
A method and an apparatus for making a pipe, and a pipe, wherein the pipe is made from a plastic feedstock pipe by expanding it against a mould. In the first step, that portion of the plastic feedstock pipe (4) which is to have a greater diameter than the rest of the pipe is partly expanded. Only after this is the entire plastic feedstock pipe (4) expanded against the mould (1).
Latest Patents:
The invention relates to a method of making a pipe having a socket.
The invention further relates to an apparatus for making a pipe having a socket, the apparatus comprising a mould and means for expanding a plastic feedstock pipe against the mould.
The invention still further relates to a pipe having a socket and made from a plastic feedstock pipe by expanding it against a mould so that a portion of the pipe has a larger diameter than the rest of the pipe.
GB 1,432,539, for example, discloses a solution for making pipes with molecular orientation from e.g. polyvinyl chloride by blowing in a mould. In said solution, a blank is inserted into the mould, heated and expanded against the mould by blowing from the inside. By simultaneously providing the pipe with a pipe socket, accurate external dimensions are obtained for the socket, but the internal, i.e. significant, dimensions remain inaccurate. At a socket to be formed at the end of a pipe, for example, the blank expands last. This causes an axial compression at the socket, which, together with a strong circumferential orientation, weakens the mechanical properties of the socket. Since the blank expands more at the socket than in other portions, the socket portion also becomes thinner than the other portions. For this reason the portion to constitute the socket is often arranged thicker than the rest of the blank, which further contributes to the socket being finished later than the rest of the plastic pipe.
WO 98/13190 discloses a solution in which compressive tension at the socket portion is reduced by axial drawing. According to the publication, at a first phase a tube blank is partly expanded along its entire length and at a second phase a casing is withdrawn to subject the tube blank to a longitudinal drawing during final expansion. Said solution is extremely complex and cumbersome to implement.
It is the object of the present invention to provide a method, apparatus and pipe, which alleviate at least some of the above drawbacks.
The method of the invention is characterized by expanding a plastic feedstock pipe partly in the portion intended to have a greater diameter than the rest of the pipe and not expanding the plastic feedstock pipe against a mould until after said pre-expansion.
The apparatus of the invention is characterized by comprising means arranged to expand the plastic feedstock pipe partly in the portion intended to have a greater diameter than the rest of the pipe, so that a pre-expansion is formed at said portion, the means for expanding the plastic feedstock pipe against the mould being arranged to expand the plastic feedstock pipe against the mould after the pre-expansion.
The pipe of the invention is characterized by the plastic feedstock pipe being expanded partly in the portion having a greater diameter than the rest of the pipe, and by the plastic feedstock pipe being expanded against the mould after said pre-expansion.
It is an essential idea of the invention that a plastic pipe is made from plastic feedstock pipes by expanding it against a mould such that pre-expansion is carried out, whereby the plastic feedstock pipe is expanded partly in the portion intended to have a greater diameter than the rest of the pipe, and thereupon the entire plastic feedstock pipe is expanded against the mould in a second step. It is the idea of a preferred embodiment that in the first step, i.e. when the socket portion is being pre-expanded, the temperature of the portion to be expanded is raised higher than the orientation temperature of the material. It is the idea of a second preferred embodiment that the socket is pre-expanded by a mechanical expanding device arranged within the plastic feedstock pipe.
It is an advantage of the invention that pre-expansion of the socket portion results in the socket portion expanding during final expansion simultaneously with or before the rest of the tube, whereby undesired axial compression in the socket portion can be reduced or eliminated. If pre-expansion is carried out at such a high temperature that it does not cause molecular orientation, the blow up ratio, i.e. circumferential orientation degree, of the socket portion can be reduced as compared with prior art solutions. In prior art solutions, the blow up ratio in the socket portion is higher as compared with the rest of the pipe, and the method of the invention allows a pipe to be provided whose blow up ratio is substantially equal along the entire length of the pipe. Pre-expanding the socket portion of a plastic feedstock pipe allows the blowing of the socket portion and its dimensions to be controlled better than previously, i.e. the desired internal dimensions for the socket portion can be provided more accurately. By implementing the pre-expansion of the socket portion by a mechanical device allows final expansion to be arranged substantially without an intermediate step after pre-expansion, whereby the pipe can be made by a simple method and the time taken by making the pipe remains relatively short. Furthermore, a mechanical pre-expanding device allows the internal dimensions of the socket portion to be expanded accurately, and in addition the rest of the pipe and the socket portion can be expanded substantially simultaneously.
The invention will be described in greater detail in the attached drawings, in which
Once the plastic feedstock pipe 4 is arranged within the apparatus, at least that portion whose diameter in the final product is to be greater than the rest of the pipe is heated e.g. by electric resistors 7 disposed in the socket support 3 or by some other suitable heating means. It is possible to heat the plastic feedstock pipe 4 e.g. by a suitable medium, arranged to circulate either outside or inside the plastic feedstock pipe 4. Medium, e.g. air, is then fed via a first inlet duct 8 or a second inlet duct 9 to the inside of the plastic feedstock pipe 4 to raise the pressure within the plastic feedstock pipe 4 such that the plastic feedstock pipe 4 is pressed against the socket support 3 as is shown in
After the pre-expansion shown in
During pre-expansion, the end of the plastic feedstock pipe 4 on the side of the socket 4b to be formed may be arranged movable such that during pre-expansion of the socket 4b portion, the wall of the plastic feedstock pipe 4 at said portion does not become substantially thinner, or it in fact thickens. The plastic feedstock pipe 4 is typically expanded to such a degree that the diameter of the finished pipe is 1.5 to 2.5 times that of the diameter of the plastic feedstock pipe 4. The body portion is preferably expanded twofold. The socket portion 4b then typically expands 2.3-fold. Pre-expansion can be used to make both the body portion 4a and the socket portion 4b expand twofold in the final expansion. A sufficient increase caused by pre-expansion in the diameter is an addition of about 10 percent. Pre-expansion may be used to expand the socket portion 4b outwards by e.g. the thickness of the wall of the plastic feedstock pipe 4.
After pre-expansion, pressure medium is supplied along the inlet duct 9 to the inside of the plastic feedstock pipe 4, whereby the plastic feedstock pipe 4 starts to be pressed against the mould 1 even at the body portion 4a. The expansion mandrel 10 is simultaneously expanded, thereby causing substantially the entire plastic feedstock pipe 4 to be pressed against the mould 1 in the manner shown in
The drawings and the related description are only intended to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims. Accordingly, pre-expansion of the socket portion may be carried out outside the mould, whereby a plastic feedstock pipe 4 pre-expanded at the socket portion 4b is introduced into the mould 1 and final expansion is then carried out.
Claims
1-6. (canceled)
7. An apparatus for making a pipe having a socket, the apparatus comprising a mould, means for expanding a plastic feedstock pipe against the mould and means arranged to expand the plastic feedstock pipe partly in the portion intended to have a greater diameter than the rest of the pipe, so that a pre-expansion is formed at said portion, the means for expanding the plastic feedstock pipe against the mould being arranged to expand the plastic feedstock pipe against the mould after the pre-expansion.
8. An apparatus as claimed in claim 7, further comprising means for raising the temperature of the material of the plastic feedstock pipe during pre-expansion higher than the orientation temperature of the material.
9. An apparatus as claimed in claim 7, wherein the means arranged to expand the plastic feedstock pipe partly in the portion intended to have a greater diameter than the rest of the pipe is a mechanical expanding device for pre-expanding the plastic feedstock pipe.
10. An apparatus as claimed in claim 9, wherein the mechanical expanding device is arranged, after pre-expansion, to expand against the mould that portion of the plastic feedstock pipe which is intended to have a greater diameter than the rest of the pipe.
11. A pipe having a socket and made from a plastic feedstock pipe by expanding it against a mould so that a portion of the pipe has a larger diameter than the rest of the pipe, wherein the plastic feedstock pipe is expanded partly in the portion intended to have a greater diameter than the rest of the pipe, and the plastic feedstock pipe is expanded against the mould after said pre-expansion.
12. A pipe as claimed in claim 11, wherein the temperature of the material of the plastic feedstock pipe is arranged to be higher during pre-expansion than the orientation temperature of the material, the blow up ratio of the entire pipe being substantially equal.
Type: Application
Filed: Dec 29, 2004
Publication Date: May 26, 2005
Applicant:
Inventor: Per Holtstrand (Sparsror)
Application Number: 11/025,176