Is crown a proper noun

No, the noun 'crown' is a common noun; a general Word for:

• a wreath or band for the head worn as a mark of victory or honor;
• a royal headdress;
• the top of the head;
• the top or highest part of something;
• a type of British coin.

A Word for any crown of any kind.

A proper noun is the name or title of a specific person, place, or thing; for example, Sheikh Hamdan bin Mohammed bin Rashid Al Maktoum, Crown Prince of Dubai, United Arab Emirates or Crown Point NY.