Cold forming of plastics part II. Draw forming of laminates containing crosslinkable core

Cold‐drawing poly(vinyl chloride) at 24°C increased the yield strength by 25 percent, modulus by 50 percent, and the ultimate strength by 100 percent. The onset of thermal shrinkage was reduced from 80°C (Tg) to 45°C. This thermal instability can be a significant disadvantage of cold‐forming for many applications. It is shown in this study that subsequent thermal treatment at 70°C (T < Tg) re‐establishes a shrinkage onset temperature of 80°C without reducing property levels. The structural changes associated with both orientation and thermal treatment were investigated using DSC, X‐ray diffraction and birefringence. Cold‐drawing produces molecular alignment as measured by birefringence and X‐ray. Thermal treatment of unstretched samples, as well as stretched samples under constraint and stretched samples unconstrained, always leads to a small reduction in free volume as revealed by a measured increase in enthalpy at Tg. However, this free volume change, produces a thermally‐stable oriented structure only when the samples are treated under constraint. Thermal treatment does not stabilize unconstrained samples. Rather it causes almost complete molecular relaxation and a reduction of physical property levels.

Section: Introductionmentioning

confidence: 99%

Thermai treatment of cold‐formed poly(vinyl chloride)

Brady

Jabarin

1977

Review of forging, stamping, and other solid‐phase forming processes

Kulkarni

1979

In the last ten years, a considerable amount of work has been conducted on many different processes distinct from common plastics processing methods such as injection molding, extrusion, and compression molding. Perhaps the most common feature of these new techniques is that they resemble more the methods used for fabricating metallic materials in solid phase. However, there is a lack of uniform terminology. More importantly, the commercial acceptance and applicability of these processes have been slow. This review attempts to summarize the important findings of various publications and, whenever possible, to give information about potential or actual industrial applications. The purpose is to provide a brief overview of the state‐of‐the‐art of the whole technology. Advantages, disadvantages, and the need for more work are pointed out as they relate to different processes and to crystalline and amorphous materials. A few instances where material was heated beyond the melting temperature by a small amount are included in the review when the processing method was similar to solid‐phase forming.

Experimental study on cold press workability of aluminum‐polyethylene sandwich laminates

Ito

Ogawa

Furuya

1981

The cold press workability of aluminum-polyethylene sandwich laminates is experimentally investigated by a deep drawing process with a conical die. "Planium" of 2 mm thickness, in which the core layer, high density polyethylene, is sandwich-laminated between two aluminum sheets, is used as a test specimen. Soybean oil is employed as a lubricant. The dimensions of the drawing die set are determined for a circular blank so that the tensile fracture of the drawn cup occurs at the top corner of the punch. The limiting draw ratio (LDR) is experimentally explored by using many blanks of various initial diameters. In general the maximum punch load in successful drawing increases linearly with increasing draw ratio. Because of the sandwich structure, the fracture of the drawn cup occurs twice. The initial fracture (LDR,,) corresponds to a fine bending fracture at the aluminum surface. The second fracture (LDR,,) is the complete fracture of the whole laminate. The effect of punch corner radius, working velocity and thickness fraction of aluminum and polyethylene on LDF& and LDR,, are studied. The strain distributions of deep drawn cup in three orthogonal directions are analyzed experimentally.