EXTERNAL CONTRACTING BRAKE-05

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External contracting brakes are mainly used in large machines and old type engines. It consists of a brake band, brake shoe and a drum.
In operation, the brake band (or shoe) of an external contracting brake is tightened around the rotating drum by moving the brake lever. The brake band is made of comparatively thin, flexible steel, shaped to fit the drum,with a frictional lining riveted to the inner surface. This flexible band cannot withstand the high pressure required to produce the friction needed to stop a heavily loaded or fast-moving vehicle, but it works well as a parking brake or hold brake.
Figure  shows an external contracting brake.The brake band is anchored opposite the point where the pressure is applied. In addition to supporting the band,the anchor allows adjustment of the brake lining clearance. Other adjusting screws and bolts are provided at the ends of the band.

ഒരു എക്സ്റ്റേണൽ കോൺട്രാക്ടിങ്ങ് തരം ബ്രേക്കിന്റെ ചിത്രമാണ് മുകളിൽ നൽകിയിരിക്കുന്നത്. ഇതിൽ വീലുമായി ബന്ധപ്പെടുത്തിയിരിക്കുന്ന ഷാഫ്റ്റിൽ ഒരു ഡ്രം നൽകിയിരിക്കുന്നു. ഡ്രമ്മിന് പുറത്തായി അകത്ത് ഘർഷണ പ്രതലത്തോടു കൂടിയ ഒരു ബ്രേക്ക് ബാൻഡ് നൽകിയിരിക്കുന്നു. കൂടാതെ ബാൻഡിനെ ഡ്രമ്മിൽ നിന്നും ഒരു റിട്രാക്ടർ സ്പ്രിങ്ങ് പുറകിലേക്ക് വലിച്ചു നിർത്തിയിരിക്കുന്നു.

ബ്രേക്ക് പെഡൽ അമർത്തുമ്പോൾ തിരിഞ്ഞുകൊണ്ടിരിക്കുന്ന ഡ്രമ്മിലേക്ക് ബ്രേക്ക് ബാൻഡ് വന്ന് മുറുകുന്നു. ബാൻഡിന്റെ ഉള്ളിൽ നൽകിയിരിക്കുന്ന ഘർഷണ പ്രതലം ഡ്രമ്മിൽ ഉരസുന്നതിനാൽ ഡ്രമ്മിന്റെ കറക്കം നിലക്കുന്നു. ബ്രേക്ക് പെഡലിൽ നിന്നും കാല് അകറ്റുമ്പോൾ റിട്രാക്ടർ സ്പ്രിങ്ങിന്റെ മർദ്ദം കാരണം ബാൻഡ് ഡ്രമ്മിൽ നിന്നും അകലു കയും ഡ്രം വീണ്ടും തിരിയുവാൻ തുടങ്ങുകയും ചെയ്യുന്നു. ഇത്തരം ബ്രേക്കുകൾ ഇപ്പോൾ വാഹന ആവശ്യങ്ങൾക്കായി ഉപയോഗിക്കുന്നില്ല.


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