Abstract: Porous pipe having a porosity which varies continuously and controllably with length is produced by extruding a mixture of particles of prevulcanized elastomer such as reclaimed crumb rubber and a thermoplastic binder such as polyethylene with all parameters controlled except for die temperature of pull-off rate. By gradually varying temperature or pull-off rate during extrusion, the porosity of the pipe gradually changes. The leak rate can be controlled in a manner to produce a length of porous pipe in which the leak rate is constant as the pressure drops over the length of the pipe.

Abstract: A mixture of virgin crumb rubber sized to between 30 mesh and 100 mesh containing less than 5%+100 fines and thermoplastic binder, such as carbon black filled polyethylene containing a coating promoter, such as a citrate salt and lubricant, such as a calcium stearate, is mixed in a vented Banburg mixer heated to at least 350.degree. F. to remove volatiles through vent before extrusion. The mixture is formed into sheet in the nip of a two roll assembly and cooled in air before diced into pellets by a dicer.The pellets are formed into porous pipe by extrusion in a pipe extruder having the feeding, transition and metering zones separately heated to temperatures from 320.degree. F. to 400.degree. F. (T.sub.1, T.sub.2, T.sub.3). The die has a separate jacket receiving heat exchange fluid for heating the die to a temperature from 290.degree. F. to 380.degree. F. to form a porous pipe having more uniformly spaced and sized pores and a smoother inner wall surface.

Abstract: A mixture of crumb rubber, binder, such as polyethylene, and slip contact agent, such as talc, and lubricant, such as a metal stearate, is formed in a blender (10), is shaped into pellets (32) by extruding a strand of the mixture (26) into water (28) and breaking the strand into pellets. The pellets (32) are adjusted to a preselected water content in drier (46) before storage in closed bags (50), stored and reinforced in a container (54).The controlled water content pellets (32) are formed into porous pipe (88) by extrusion in pipe extruder (62) having the feeding, transition and metering zones separately heated to temperatures from 320.degree. F. to 400.degree. F. (T.sub.1, T.sub.2, T.sub.3). The die has a separate jacket (90) receiving heat exchange fluid for heating the die (68) to a temperature from 290.degree. F. to 380.degree. F. to form a porous pipe (88) having more uniform porosity. Porosity is controlled by selecting water content of the pellets and controlling die temperature.